Conventional lighting devices generally use incandescent lamps or fluorescent lamps, and operations of such devices include light-on, light-off, brightness adjustment by adjusting output, and lighting of a night-light (tiny lamp).
Recently, because of remarkable developments of light emitting diodes (LEDs), LEDs of high brightness and high output with various output wavelengths come to be practically used. A lighting device using such LEDs allows, in addition to the light-on and light-off operations, the user to flexibly change color tone of illumination, as LEDs having different wavelengths are combined and respective outputs can be adjusted. It is difficult, however, to adjust the LED outputs to attain favorable color tone, for a person not having any knowledge of optical or illumination field. Therefore, some scheme that facilitates light adjustment is desirable.
Light environment has significant psychological and biological influences on humans. Therefore, appropriate design of light environment is one of basic elements to attain healthy and comfortable living environment.
In this regard, a light environment that combines illumination and the phase of autonomous, intrinsic rhythm (biological rhythm) of a human is desirable, for one to enjoy healthy and comfortable life.
Japanese Patent Laying-Open No. 2000-294384 proposes a method of switching two fluorescent lamps having different color temperatures in accordance with time zone.